The invention relates to a valve control device for a gas exchange valve of an internal combustion engine, comprising a cam follower lever interacting with a camshaft and a rocker arm that is contacting the cam follower lever and that actuates the valve. The rocker arm is adjustable for valve lift adjustment by means of an adjusting device.
Mechanically fully variable valve control devices are known and are employed for reducing fuel consumption in internal combustion engines of passenger cars (DE 101 40 635 A1). The cam follower lever is pivotable about an axis and is positioned with a first roller on a guide and with a second roller on an adjusting device that is in the form of a slidable adjusting bar. For changing the valve lift, the adjusting bar is displaced and the cam follower lever adjusted thereby. The rocker arm is resting on the cam follower lever. The rocker arm is supported with a first lever end on the cylinder head of the internal combustion and actuates with a second lever end the gas exchange valve. As the camshaft rotates, the cam follower lever moves by means of a roller along a curved path of a guide provided at the cylinder head. The manufacture and support of the guide are complex. Extremely high engine speeds are not possible because the main mass of the cam follower lever is high. Mounting of the guide in the cylinder head is also very complex.
A further valve control device (DE 41 12 833 A1) is known in which the cam follower lever and the rocker arm are formed by two pivotably supported single-arm levers. The cam follower lever is connected with one end rotatably on an eccentric whose eccentric shaft is eccentrically supported in an actuator that is rotatable about a fixed axis associated with the cylinder head. The cam follower lever is resting on the rocker arm which, in turn, is also pivotably supported about a fixed axis that is associated with the cylinder head. By means of the eccentric, the cam follower lever is linearly displaced and in this way the valve lift is adjusted. The adjusting device with the eccentric and the actuator is very complex and expensive. During adjustment, a significant friction force is produced so that the potential for reducing consumption of the internal combustion engine is limited. The eccentric of the adjusting device enables moreover only a minimal adjusting travel so that the valve control device is not suitable for large valve lift adjustments. A lift adjustment of only approximately 50% of the maximum lift can be achieved.
In another known valve control device (US 2005/0028766 A1), the rocker arm is pivotably supported about an axis. In order to adjust the valve lift, the axis of rotation of the rocker arm or the axis of rotation of the cam follower lever is moved. The movability increases the constructive expenditure of the valve control device. The rocker arm and the cam follower lever are contacting each other with curved control surfaces that are substantially positioned at a slant to the valve axis. This causes significant friction forces when the valve control device is operating. Due to the adjustable elements, the valve control device does not operate at a low noise level.
In a further known valve control device (US 2006/0021590 A1), the rocker arm is pivotably supported in the cylinder head and is resting on the valve to be actuated. The cam follower lever is designed as a rocker lever that is rotatably supported about a central axis. The axis of rotation of the cam follower lever can be moved along a guide that is secured on the cylinder head in order to adjust the valve clearance. The valve control device has therefore a complex and failure-prone configuration.
Also, a valve control device is known (DE 29 51 361 A1) in which the rocker arm is pivotably connected at one end to a slide that is slidable transverse to the axis of the valve for valve lift adjustment. For this purpose, a complex adjusting drive is required.